(1) Field of the Invention
The present invention relates to a display device comprising TFTs (Thin Film Transistor) that use oxide semiconductors.
(2) Description of the Related Art
A liquid crystal display device has a TFT substrate, a counter substrate opposing to the substrate and a liquid crystal layer, sandwiched between the TFT substrate and the counter substrate. The TFT substrate has plural pixels; each of the pixels has a pixel electrode and a thin film transistor (TFT). A transmittance of light in each pixel is controlled by liquid crystal molecules; thus, images are formed. On the other hand, the organic EL display device has a self-illuminant organic EL layer, a driving TFT, and a switching TFT in each pixel; thus, color images are formed.
The oxide semiconductor has a high OFF resistance, thus, if it is used in the TFT, OFF current can be decreased.
The patent document 1 (Japanese patent laid open 2008-294136) discloses the structure that a high resistance metal oxide is formed on the substrate; a part of high resistance metal oxide is decreased in resistance to form the semiconductor, and then, the semiconductor is used as the TFT. The portion of the metal oxide whose resistance is not decreased is used as a separating region between the elements.